The present invention relates to novel methods and devices for producing solid subassemblies of fluidic particulate matter by creating a slurry that can be frozen. Preferably this invention allows the production of subassemblies of solid media to be used for manufacturing electrodeionization devices.
The term xe2x80x9celectrodeionizationxe2x80x9d refers to a process of reducing the concentration of ions in a liquid, with the liquid generally being water. This process, as opposed to other types of processes that provide the same result (distillation, electrodialysis, reverse osmosis, liquid chromatography, membrane filtration and ion exchange) is characterized by an ion exchange material, anion and cationic membranes in which the resin is placed between, and electrodes for providing direct current.
For purposes of this invention, the term xe2x80x9cmediaxe2x80x9d is defined as particulate matter with fluid characteristics that is used in connection with fluid purification or separation. Such media include, but are not limited to, ion exchange resins, both singular and mixed, activated carbon beads, chromatography beads and related materials.
For purposes of this invention, the term xe2x80x9cparticulate matterxe2x80x9d will mean any solid, granular material, including powders and other finely divided solids, that have fluid characteristics.
The use of ion exchange resins for the ion exchange material for electrodeionization is well known in the art. Kollsman, U.S. Pat. No. 2,815,320, describes the use of macroporous beads formed of ion exchange resins positioned between the anionic and cationic membranes. Kollsman teaches that these ion exchange resin beads act as a path for ion transfer and also serves as an increased conductivity bridge between the membrane for the movement of ions.
Further development in the art has resulted in additional types of media being used in electrodeionization devices. Denoncourt, et al., U.S. Pat. No. 5,593,563, disclose the use of electron conductive particles in the cathode compartment of an electrodeionization device. Unfortunately, for either type of media, the prior art does not provide an elegant and cost effective manner of loading the media into the compartments of electrodeionization devices.
Spacers, filled by way of the present invention, were first disclosed in Siu, et al., U.S. Pat. No. 4,747,929. The patent provides spacers that retain ion exchange media while promoting a substantially uniform flow of liquid through the compartments created by spacers being bonded to each other.
The ELIX(copyright) water. purificationsystem Millipore Corporation, Bedford, Mass.) includes electrodeionization device. Prior to the conception and reduction to practice of the present invention, the production of the device, and specifically the fabrication of the resin-filled cell pairs and cell stacks, was quite labor intensive.
For producing a prior art resin filled cell pair, a conditioned anion membrane is affixed to one side of a spacer. Spacers could consist of any shape but the spacers used for producing the ELIXelectrodeionization device in the unit are rectangular in shape and are characterized by a rectangular orifice contained therein.
With the addition of the membrane, a trough-like channel is formed which can receive media. The channel is then filled with resin by hand packing the resin in the channel with a stainless steel spatula. Then, running the stainless steel spatula across the top surface of the dilute spacer, the excess resin is removed. The worker must then inspect the resin-filled spacer to insure that the channel is uniformly filled. Any resin remaining on the surface of the spacer must then be removed. The exposed resin-filled channel is then covered by a conditioned cation membrane, which is fixed to the body of the spacer in a manner that does not allow resin to leak out. The worker must then re-inspect the filled cell and remove any excess resin from its external surfaces.
Recently, new methods of manufacturing electrodeionization devices have been disclosed by A. Proulx, U.S. application Ser. No. 08/656,138, filed May 31, 1996 and issued on Oct. 28, 1997 as U.S. Pat. No. 5,681,438. Proulx discloses improvements to the manufacturing process of electrodeionization devices but, despite these improvements, the difficulties with hand packing resin remain.
Using the method disclosed by Proulx, the resin spacers are packed with resin as the device is built. This requires the module to sit inside a welding machine and the operator to weld each spacer as it is added to the stack. Because of the time needed to hand fill the spacer channels while the modules are in the welder, the welder is idle for a significant time period during the process. This process prevents more than one operator from using a welder at a time, or at a minimum, prevents the efficient use of such a welder. The ability of two operators to share a welder would dramatically decrease the cost of producing the device.
Previous methods used to fill the spacer channels included a slurry-fill technique. The resin was mixed with an excess amount of water and delivered to the channel from a pressure vessel. To insure proper settling of the resin, excess water was continuously removed from the spacer channel. This method proved to be undesirable for many of the reasons provided above, but also required the capital expense of the pressure vessels to deliver the slurry as well vacuum devices for removing the excess water.
There are additional means of preparing molded ion exchange resin. Tennison et al., U.S. Pat. No. 5,622,997, issued Apr. 22, 1997, discloses a process for preparing a molded exchange resin structure from ion exchange resin precursor. In this process, the precursor resin is compressed into shape. Then, the functional groups are chemically bonded to each other. In the preferred embodiment, this process required a hydraulic press. A more elegant, cost-effective method which uses standard media is desirable.
A related method of solidifying ion exchange media is also disclosed by Roberson et al., U.S. Pat. No. 4,585,583. This method, however, is directed to solidifying spent ion exchange media, not media intended for ion exchange.
An additional method for introducing and removing ion exchange resign and other particulate matter from an electrodeionization device is disclosed in U.S. Pat. No. 5,120,416 issued to Parsi et al. This patent disclosed an apparatus for pumping a slurry into a pre-assembled electrodeionization stack.
However, none of these methods allow for producing an electrodeionization device quickly and with a precise volume of ion exchange media. Accordingly, it would be desirable to have a novel method of preparing and packing media into predetermined shapes. It would further be preferable to have a novel method of preparing and packing media into predetermined shapes, which makes assembly of an electrodeionization device faster and with more efficient use of capital equipment.
The present invention provides a novel method of solidifying particulate materials, and specifically media for use in manufacturing processes. The present invention further provides methods of manufacturing electrodeionization device subassemblies of spacer/media for electrodeionization compartments. The compartment subassemblies result in fewer man-hours needed to manufacture the modules and allow for a more efficient use of capital equipment. The present invention provides a method of producing media in a predetermined, solid shape from media and liquid, the method comprising inserting media into a pre-selected mold; adding liquid to the media to create a slurry; and placing the filled mold into an environment that will freeze the liquid.
An advantage of the present invention is that media to be used in the electrodeionization manufacturing process is placed in a slurry that is then frozen. The solid object that results from the method improves handling of media during the manufacturing process. Moreover, the chance of particulate media getting on membrane or spacer bond areas is minimized. Such excess resin can reside on the spacer where the membrane is bonded and can contribute to product failures. In addition, when frozen, the media does not shift or change distribution while the electrodeionization module is manufactured. Lastly, decoupling of the filling of electrodeionization compartments from the balance of the manufacturing process improves the efficiency of manufacturing these devices.
The present invention also provides a method of uniformly distributing the packing density of media used in manufacturing electrodeionization devices, the method comprising inserting media into a receptacle designed to hold such media; inserting an amount of liquid effective to level the upper surface of the media; and vibrating the receptacle with a vibrating device for a time sufficient to distribute the media such that its packing density is substantially uniform.
The principal prior art methods of spreading media in electrodeionization devices were hand spreading and delivery via a pumping and piping system. The present invention of vibrating the media increases the packing density of the media. Moreover, the packing density of vibrated units as opposed to hand packed units have greater consistency. One of the problems with hand packing media in spacers is that there is significant variability from operator to operator. The present invention substantially limits such variability.
The present invention further improves the manufacturing process. First the media can be formed in a cavity or mold of predetermined shape. Accordingly, the dimensions and flatness of the slurry brick transferred to a spacer can be made with closer tolerances. Alternatively, the spacer can be filled with a pattern of a number of slurry bricks, that is, at least two, rather than merely one. For example, on larger units, it may be appropriate to use a number of bricks that can be laid in a pattern in the spacer channel, rather than a single brick, to fill it. Since the brick thaws after assembly of the electrodeionization devices, use of such multiple brick assemblies would not affect packing density.
The use of frozen media rather than hand packed media allows the manufacturing process of the electrodeionization modules to be altered in a manner that improves the efficiency of the process. With the hand packed media, the spacer was filled, stored then welded together at final assembly. With use of the frozen media, the spacer is not handled with resin inside of it, therefore it easier to handle and store.
The present invention further provides a method of manufacturing an electrodeionization module, the method comprising preparing a slurry including water and ion exchange resin; pouring the resin slurry into a spacer channel mold; freezing the resin slurry until solid; fixing a first spacer plate onto an end cap, wherein the spacer plate has a channel; inserting frozen resin slurry into the spacer plate channel; and fixing an end cap on the end opposite the first end cap. In a preferred embodiment, the method of the present invention further comprises preparing a slurry including water and activated carbon beads; pouring the carbon slurry into a spacer channel mold; freezing the carbon slurry until solid; fixing a final spacer plate onto the last resin-containing spacer plate fixed to the module; inserting frozen carbon slurry into the channel of the final spacer plate; and fixing a second end cap to the final spacer plate.
The present invention also provides a receptacle or mold for freezing a slurry including media and liquid. Such a mold would be comprised of materials that can withstand freezing the liquid and have walls and a base configured such that the internal shape of the mold is substantially similar to a compartment designed to receive media. In a preferred embodiment, the bottom, internal surface of the mold would be uneven. In a still more preferred embodiment, the bottom, internal surface of the mold would be scored. In a preferred embodiment, the scoring would be substantially parallel.
The present invention also provides a method of manufacturing a subassembly for a device that contains particulate matter in a compartment, a method comprising: preparing a slurry including liquid and the particulate matter; transferring the slurry into a mold configured to produce a slurry brick that is substantially equivalent to a space in the compartment designed to receive the particulate matter; freezing the slurry until a slurry brick is created; and transferring the slurry brick into the compartment. Preferably, the method further comprises vibrating the slurry-filled mold prior to freezing the slurry to increase the packing density of the media as well as consistently distribute the particulate matter in the slurry.